Objective: To examine the prevalence of an anterior ethmoidal artery (AEA) that located below the skull base and the locations in relation to fixed anatomical structures.
Material and Method: Computed tomography (CT) data relating to paranasal sinuses of 100 consecutive patients were
obtained using a 128 multidetector high-resolution CT scanner (Phillips®). Thin slice axial CT was performed and images in
coronal and sagittal planes were reconstructed. Entrance and exit points of the AEA were determined. Locations of AEAs in
relation to the skull base were assessed independently by two assessors. The distance between the AEA and the skull base, the bulla lamella/the anterior wall of ethmoidal bulla (BL/AWEB) and the vertical basal lamella of the middle turbinate (BLMT)
were measured.
Results: The AEA was found to locate below the skull base in 72.5%. The mean distance between the AEA and the skull base
was 3.2 mm. Nearly 95% of the AEAs were located between the BL/AWEB and the BLMT, and only 5% was at or behind the BLMT. 71.0% of the AEAs located posteriorly to the midpoint of the distance between the BL/AWEB and the BLMT. The mean
distance from the BL/AWEB was 7.3 mm.
Conclusion: Most of the AEAs located below the skull bases in Thais and being posteriorly to the midpoint of the distance
between the BL/AWEB and the BLMT. The BLMT and the BL/AWEB were two fixed constant anatomical features that may be used as optional landmarks for endoscopic localization of the AEAs.

Keywords: Anterior ethmoidal artery, skull base, bulla lamella, middle turbinate